running cdk bootstrap with an existing cdk.json fails attempting to execute `app`

### Describe the bug

I have a `cdk.json` file in my directory with the following contents

```
{
"app": "tsx cdk.ts",
"debug": true
}
```

When I try to run bootstrap in this directory with `pnpm dlx` I receive an error saying `tsx` is not found.

```
➜ pnpm dlx aws-cdk bootstrap aws:///us-east-1
o
/bin/sh: tsx: command not found

Subprocess exited with error 127
```

Unlike `npx`, `pnpm dlx` (and similar with yarn) will reach out to the registry to execute instead of the local node_modules. Granted I do have the CLI in this project locally, but I thought it was odd to receive this error when running bootstrap

### Regression Issue

- [ ] Select this option if this issue appears to be a regression.

### Last Known Working CDK Version

_No response_

### Expected Behavior

running `cdk bootstrap` does not execute the app

### Current Behavior

see description

### Reproduction Steps

1. `pnpm init`
2. add cdk.json from description
3. run `pnpm dlx aws-cdk bootstrap ...`
4. observe error

### Possible Solution

_No response_

### Additional Information/Context

_No response_

### CDK CLI Version

2.154.1 (build febce9d)

### Framework Version

_No response_

### Node.js Version

22.x

### OS

macos

### Language

TypeScript

### Language Version

_No response_

### Other information

_No response_